The invention relates to fuel systems for internal combustion engines, and more particularly to filters used in the fuel systems.
It is known to utilize filters in fuel systems for internal combustion engines to filter debris from the fuel. Return-type fuel systems have, upstream of the fuel manifold, a filter that filters the fuel before it enters the fuel manifold. Fuel that is not injected into the combustion chamber exits the fuel manifold and returns to the fuel tank via a return line.
Mechanical returnless fuel systems for internal combustion engines are also known. Unlike return-type systems, mechanical returnless fuel systems have return lines either within the fuel tank or just outside the fuel tank. In such systems, fuel is pumped from the fuel pump to a pressure regulator. The pressure regulator directs the proper amount of fuel required by the engine to the fuel manifold for injection into the combustion chambers. On its way to the fuel manifold, the fuel to be used passes through a fuel filter just as with return-type systems. Fuel not needed by the engine is directed by the pressure regulator to a return line which routes the fuel back to the fuel tank.
In the past, fuel passing through the return line of a mechanical returnless fuel system has not been filtered. Recirculation of the unfiltered return fuel was found to decrease the life of the fuel pump and shorten the life of the fuel pump inlet filter due to the debris generated by the wear of internal fuel pump components. As such, fuel system suppliers have begun to add a return line fuel filter in mechanical returnless fuel systems to improve the fuel pump and fuel pump inlet filter durability.
Adding a fuel filter to the return line of returnless fuel systems has improved the durability of the fuel pump and fuel pump inlet filter, but has caused other problems. Specifically, no provision has been made for handling plugged return filters. If the return filter plugs, the pressure in the fuel system will increase until reaching the fuel pump relief valve setting (typically 5.5-6.5 bar), at which point the fuel pump will shut down and the engine will stop. The driver will not be warned of the upcoming engine shutdown as the engine control computer can compensate for the increased fuel system pressure.
Another problem would occur during engine shutdown/hot soak. During engine shutdown, the hot gasoline inside the engine fuel manifold is normally allowed to expand back through the pressure regulator and into the fuel tank. Since the expanding fuel is not allowed to return through the fuel pump, due to a check valve inside the fuel pump that maintains the prime of the fuel pump during shutdown, the expanding fuel must return via the return line. If the return filter is plugged, the expanding fuel cannot return to the fuel tank and has nowhere to go. The pressure will build until a failure occurs somewhere in the fuel system. This type of failure provides a strong potential for a dangerous external fuel leak.
The present invention alleviates pressure build-up problems in fuel systems by providing a self-relieving fuel filter assembly. The self-relieving fuel filter assembly is preferably positioned in the return line of a returnless fuel system and allows for filtered return flow without the dangerous risks associated with pressure build-up leading to engine shutdown and/or external fuel leaks. Under normal conditions, the self-relieving fuel filter assembly filters the fuel in the return line, thereby improving the life of the fuel pump and fuel pump inlet filter. If the filter plugs however, its self-relieving characteristic enables fuel to pass through unfiltered and return to the fuel tank before dangerously high pressures are reached in the fuel system. Catastrophic failures due to high fuel system pressure are avoided in favor of less dangerous and more gradual system degradation type failures, such as plugged fuel pump inlet filters and worn-out fuel pumps.
More specifically, the invention provides a fuel system for an internal combustion engine, the fuel system including a fuel tank, a fuel pump communicating with the fuel tank, a fuel manifold downstream of the fuel pump, and a return line downstream of the fuel pump, the return line communicating with the fuel tank. The fuel system also includes a self-relieving fuel filter assembly having a filter member. The self-relieving fuel filter assembly communicates with the return line and is variable between a first state, wherein fuel passes through the return line and the filter member before returning to the fuel tank, and a second state, wherein fuel passes through the return line without passing through the filter member before returning to the fuel tank. The self-relieving fuel filter assembly therefore permits the continuous passage of fuel through the return line even when the filter member becomes plugged.
Preferably, the fuel system is a mechanical returnless fuel system having a pressure regulator downstream of the fuel pump and upstream of the return line. The self-relieving fuel filter assembly is variable from the first state to the second state when the fuel pressure in the return line exceeds a predetermined pressure.
In one embodiment, the filter assembly includes a blow-out plate adjacent the filter member. The blow-out plate is alterable from an intact condition, wherein fuel cannot flow through the plate, to a blown-out condition, wherein fuel can flow through the plate. Preferably, the blow-out plate comprises a plastic member having a relatively thin cross-sectional thickness. Additionally, the plastic member can be scored to help initiate the blow out.
In another embodiment, the filter member is in the return line and the self-relieving fuel filter assembly further includes a bypass line having a pressure relief valve that allows fuel to bypass the filter member.
In another embodiment, the self-relieving fuel filter assembly is in effect a pressure relief valve in which the filter member is a movable valve member biased against a valve seat. The assembly thus includes a spring connected to the filter member. The spring biases the filter member against a seat such that the fuel must flow through the filter member when the filter member is seated. The filter member moves off the seat when the filter member is plugged and the fuel pressure in the return line reaches a predetermined pressure. This allows fuel to flow around the filter member.
Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings.